import java.util.Scanner;

public class java_4 {
	public static void main(String[] args) {
		System.out.println("请输入购买的长度");
		Scanner input = new Scanner(System.in);
		double a = input.nextInt();
		if (a % 3 != 0) {
			int b = (int) (a / 3);
			int c = b + 1;
			System.out.println(c);
		} else {
			System.out.println(a / 3);
		}

	}
}
